Glass bottles have long been seen as the gold standard for storing drinking water for their eco-friendly, chemically inert, and reusable qualities. However, recent findings suggest they may not be as harmless as they appear. While the glass itself poses no risk, it’s the painted metal caps that are under scrutiny. According to a 2025 study by ANSES, a French Agency for Food, Environmental and Occupational Health & Safety, “painted coatings inside the caps of glass bottles are the primary source of microplastic contamination in bottled water.” These caps can degrade over time, releasing microscopic plastic particles into the liquid. Water stored in such bottles was found to contain up to 4.5 microplastic particles per litre — nearly three times higher than in plastic bottles.
All glass is not equal – which types are safe?
Regardless of the glass type, the risk of contamination is reduced if the bottle has a plastic or uncoated metal cap instead of a painted one Shutterstock
Glass bottles, particularly those with painted metal caps contain more microplastics (~4.5 part/L) than plastic bottles (~1.6 particles/L). The source of microplastic particles is the painted cap coatings and not the glass,” said Tejas Gohel, consultant microbiologist, Lilavati Hospital, Mumbai.
The grade and quality of glass used for bottles also matter significantly. Borosilicate glass is a better and safer choice as it is more resistant to thermal shock and chemical leaching. Soda-lime glass, commonly used in cheaper bottles, is more prone to breakage and may react with certain liquids over time, especially if not properly tempered. Regardless of the glass type, the risk of contamination is reduced if the bottle has a plastic or uncoated metal cap instead of a painted one. The bottles with food-grade markings are better than those that are decorative or cheaply made.
Gohel further said, “The health implications of this return to chronic microplastic ingestion may lead to inflammation or endocrine disruption, but it remains uncertain. It is advised to choose a bottle with unpainted or plastic caps.”
What you store in your bottle also matters
Acidic drinks can cause faster degradation of bottle caps or leach unwanted elements from lower-quality glass. Even oils and fruit infusions, when stored for long durations, can alter the chemical stability of the container Shutterstock
“Plastic nowadays is always a big ‘No’. Glass bottles with an unpainted or plastic cap are medically safer than polypropylene (PP) bottles. PP bottles release 100-240 microplastic particles per litre with repeated use, and millions when heat is applied, during sterilisation. These microplastics can migrate across gut barriers or induce inflammation,” said Gohel.
While water is generally safe in a glass, not all liquids interact the same way. Acidic drinks such as lemon water, soda, or vinegar-based solutions can cause faster degradation of bottle caps or leach unwanted elements from lower-quality glass. Even oils and fruit infusions, when stored for long durations, can alter the chemical stability of the container, especially if the bottle is exposed to sunlight or heat. As a rule of thumb, store only plain water in your glass bottle, and clean it regularly to prevent microbial growth, especially around the cap area.The microbiologist elaborated that “glass bottles release only approximately ~4.5 particles/L, and most are from the coating of the cap.” “It is always good to use glass for storing water and not to use hot water when storing liquids in PP bottles,” he added.
Are there better alternatives to glass?
When it comes to safety and durability, stainless steel is often the best long-term alternative Shutterstock
When it comes to safety and durability, stainless steel is often the best long-term alternative. It is inert, corrosion-resistant, and completely free from microplastics and chemical leaching. Food-grade copper bottles offer additional health benefits such as antimicrobial properties and immunity boosting, but must be used with caution — they can leach heavy metals into the water if stored too long or used with acidic drinks. For short-term water storage, copper is a great option if water is left standing for over six hours, allowing natural purification. Aluminium, though recyclable and lightweight, is more prone to denting and is typically lined with plastic, which may defeat the purpose of avoiding leaching altogether.
“It is suggested to use stainless steel products for long-term use and food-grade copper for short-term water storage, which mitigates long-term exposure to unwanted contaminants, thus safely improving the act of drinking from a bottle. Copper bottles also boost immunity and are a natural purifier when water is stored for more than six hours,” concluded Gohel.
Glass bottles still offer several benefits — they are eco-friendly, preserve the taste of water, and are safe when made with the right materials and components. However, they are not foolproof. To make a healthier choice, ensure your glass bottle is of high-grade material and paired with a plastic or unpainted cap.
MS Purkait, medical superintendent, Techno India DAMA Hospital, said, “Glass bottles retain the original taste of the water and do not leach harmful chemicals, unlike plastic bottles. It is completely recyclable and eco-friendly. Plastic bottles, on the other hand, leach chemicals, are not eco-friendly, and also impart a certain chemical taste. Liquids remain fresh for a longer period and remain cooler for a longer period in comparison to plastic bottles. Plastic bottles cannot be exposed to direct sunlight. When it comes to feeding bottles, it is better to use glass feeding bottles for babies.”